茶叶中铅含量的测定

目的建立高效、准确的茶叶中铅含量测定方法。方法采用干法灰化、湿法消解和微波消解3种方法处理茶叶样品,并使用石墨炉原子吸收光谱法和电感耦合等离子体发射光谱法(inductively coupled plasma atomic emission spectrometry,ICP-OES)分别对茶叶样品中铅含量进行检测,并对各检测方法进行比较分析。结果在铅含量的检测区间内,ICP-OES法的最低检出限比石墨炉法高20多倍。使用石墨炉法检测,3种消解方法的加标回收率顺序为:微波消解法湿法消解干法灰化。结论微波消解-石墨炉法高效、准确、可靠,可用于茶叶中铅含量进行检测。     

Tracking residual organochlorine pesticides (OCPs) in green,herbal, and black tea leaves and infusions of commercially available tea products marketed in Poland

The content of residual organochlorine pesticides (OCPs) was examined in green, herbal, and black tea leaves as well as in their infusions prepared from tea products marketed in the main supermarkets in Poland. It was found that the detected mean levels of organochlorine residues in tea leaves ranged from ?1 dry weight. Among hexachlorocyclohexane isomers, γ-HCH in green tea occurred in the highest concentrations. Among dichlorodiphenyltrichloroethane (DDT) metabolites the highest level of p,p′DDT (1.96 ng g^?1 dw) was in green tea samples. The transfer of OCPs from tea leaves to brew was investigated. The present study revealed that during the infusion process, a significant percentage of the residues, particularly pesticides with high water solubility, were transferred to the infusions. The obtained results show that the percentage transfer of each pesticides from tea to the tea infusions ranged from 6.74% (heptachlor) to 86.6% (endrin). The detected residues were below current MRLs for these pesticides.     

Profiling elements in Puerh tea from Yunnan province,China

ABSTRACT

Puerh tea, as the most representative Chinese dark tea, has attracted global interest in recent years. Profiling the levels of metal elements in Puerh tea is very important since its presence is related to human health. In this study, 41 elements in 98 Puerh tea samples from Yunnan province, China including Puerh raw tea and Puerh ripe tea were evaluated by microwave digestion combined with inductively coupled plasma mass spectrometry . The content of toxic elements, essential elements and rare earth elements of Puerh tea from different regions was discussed in detail. The concentrations of Ba, Cr, As, Pb, Bi, Fe, Zn, V, Mn, Be, Ag and Tl showed significant differences (p < 0.05) by ANOVA analysis. Principal component analysis and linear discriminant analysis were used to describe the relationship of Puerh tea from different regions. This study provided a comprehensive database for Puerh tea quality control and intake risk assessment.     

How manufacturing processes affect the level of pesticide residues in tea

Tea (both green and black) is consumed throughout the world, both for pleasure and therapeutic purposes. Most people will be unaware of their involuntary exposure to residues of pesticides lingering in processed tea and so possibly transferring into infusions of tea. The purpose of this work was to study the effect of green tea and orthodox black tea manufacturing processes on the fate of pesticides sprayed onto tea bushes (Camellia sinensis). The fates of residues of dimethoate, quinalphos, dicofol and deltamethrin in these two different types of tea manufacturing processes were compared. For black tea, the manufacturing process involves leaf harvesting, withering, rolling, fermentation and drying; and for green tea, leaf harvesting, microwave heating, rolling and drying. The two processes resulted in the same concentration factor of plant material into the dried commodity, while the decreases in residue levels were different for different pesticides. Initial microwave heating and dehydration in the green tea manufacturing process resulted in greater loss of pesticide residues than did withering and dehydration in black tea; no significant reduction in residue level resulted from the rolling and fermentation steps in black tea. Residue levels in both green and black teas were reduced during final drying. Copyright © 2004 Society of Chemical Industry     

Total content and speciation of aluminium in tea leaves and tea infusions

A total of 29 tea samples of different origin, 13 green tea samples, 13 black tea samples, two semi-fermented and one white tea, imported to the Czech Republic, were collected and analysed for total content of aluminium (Al) in tea leaves and tea infusions, as well as for Al compounds in these infusions. The total content of metals in tea leaves differs according to the type of tea (green or black) and is probably influenced by many factors, e.g., soil properties. The HPLC/IC speciation of Al in tea infusions was performed for all samples. The addition of Al³⁺ to the tea infusion proved that Al³⁺, Al(Y)²⁺ and Al(X)¹⁺ species can be determined in tea infusions. Increased extraction time did not show any affect on Al speciation, neither did the addition of sugar. After the addition of lemon juice, the speciation changed in one sample of black tea and five samples of green tea. These findings suggest that lemon juice as an additive can significantly influence Al speciation in tea infusions.     

Persistence of acetamiprid in tea and its transfer from made tea to infusion

Acetamiprid, a new-generation, highly active neonicotinoid insecticide has been used to control mites and insect pests. In the present study, the disappearance trend of acetamiprid residue in tea under field conditions was studied at two dosages for two seasons (dry and wet), and transfer of residues from made tea to infusion was also determined. Acetamiprid dissipation rate was found to be faster in the wet season. Half-life of acetamprid was found to be 1.82–2.33 days in green tea shoots and 1.84–2.25 days in made tea for both dry and wet seasons. The percent transfer of acetamiprid residues from made tea to infusion was 36.84–50.00%; however, 31.11–44.40% of the residues remained stuck to the spent leaves during both the dry and wet seasons. On the basis of transfer of residues from made tea to infusion, a waiting period of 15 days for tea plucking after pesticide application at recommended dose may be suggested.     

微波消解-电感耦合等离子体发射光谱(ICP-OES)测定茶叶中多种微量元素

采用微波消解和ICP-OES对茶叶中10种微量元素进行了分析测定.拟定了测定方法,加标回收率在95.4％～102.4％之间,相对标准偏差(n=6)在0.75％～3.89％之间,满足分析要求.为茶叶中微量元素的检测分析提供了快速准确的测定方法.     

富硒茶叶中硒含量的检测及相关标准的分析探讨

目的检测富硒茶叶的总硒含量,剖析硒含量和标示值存在的问题,梳理富硒茶的相关标准,总结潜在质量安全监管问题。方法采用微波消解法处理样品,利用氢化物原子荧光光谱法测定富硒茶样品的硒含量,分别与普通茶叶测定值和产品标示值进行对比分析。梳理了食品中硒的国家标准和富硒茶相关的地方标准、行业标准,指出了富硒茶产业关键标准的缺陷可能导致潜在的质量安全问题。结果富硒茶存在硒含量太低、达不到行业标准要求的问题,产品标示值不准确、不规范。富硒茶产业发展迅速,但其质量问题未引起足够重视,关键技术规范和国家标准缺失,对其质量监测的检验和评估仍不足。结论富硒茶相关的标准不统一,尚缺乏国家标准的规范。应尽快制定相关的国家标准,加大对该产业的监管力度,保证人们饮用健康。     

Temperature dependence of copper,iron, nickel and chromium transfers into various black and green tea infusions

Transfer ratios of copper, iron, nickel and chromium from 10 blended, unblended, instant and green tea samples of Turkish or British origin into the infusions have been determined at different brewing temperatures (18, 40, 60 and 80°C). The transfer ratio of each metal into the infusion appeared to be dependent on both temperature and strength of infusions as well as the kind of tea. Ingested metal amounts were calculated and discussed. © 1998 SCI.     

茶叶中铝、铅、砷、汞、铬、镉含量的分析及危害评价

目的研究福建省市售茶叶中金属元素含量情况,通过分析茶叶中重金属含量情况,评估其对人体的健康风险情况。方法在福建省市场随机抽取不同品种茶叶98份,用微波消解法处理茶叶,电感耦合等离子体质谱法(inductively coupled plasma mass spectrometry,ICP-MS)检测茶叶中铝、铅、砷、汞、铬、镉的含量。结果98批市售茶叶中的铅、砷、汞、铬、镉5种重金属元素含量都在国家标准范围之内,目前暂无茶叶中铝含量相关限量标准,但其危害作用有限。98份市售茶叶中铅、砷、铬、铝检出率均为100%,铬、汞的检出率分别为95.9%、37.8%。各元素靶标危害系数(target hazard quotient,THQ)排名依次为铝>铬>砷>铅>镉>汞,危害指数(hazard Index,HI)为0.2589,铝对危害指数的贡献率为45.2%。按照不同茶叶种类进行分类,其危害指数排名依次为黑茶>乌龙茶>绿茶>红茶。按照茶叶产地进行分类,其危害指数排名依次为云南>福建>浙江。结论福建省市售茶叶中这6种金属元素存在一定程度的污染,但危害指数为0.2589,小于1,对人们的健康风险较低,但仍应持续监测茶叶中金属元素的含量情况。     

六堡茶茶汤中胶体颗粒及沉淀性状研究

黑茶主要由微生物发酵形成,六堡茶是典型的黑茶之一,发酵对茶汤胶体性质与茶乳酪的成分组成是否有影响,尚未明确。本文通过动态光散射、扫描电子显微镜和高效液相色谱等方法比较了六堡茶毛茶以及发酵后的成品茶茶汤的胶体颗粒性质。结果表明,六堡茶毛茶和成品茶的茶汤均存在丁达尔现象,即存在胶体体系。两种茶汤在冷却过程的浊度变化率逐渐减少,接近常温时,成品茶茶汤浊度增加率小于毛茶;两种茶汤中均存在球形或椭球形的胶体颗粒,且胶粒粒径与Zeta电位具有温度响应。室温下成品茶茶汤的胶体颗粒平均粒径(2131 nm)显著低于毛茶(3045.8 nm),成品茶Zeta电位绝对值(-24.8 mV)高于毛茶(-19.2 mV)。两种茶汤成分差异导致二者沉淀差异,成品茶固形物相对沉淀率(2.22%)少于毛茶(2.79%),成品茶沉淀主要成分为茶红素、茶褐素和多糖,占沉淀94.11%,毛茶则为多酚、蛋白质和多糖,占沉淀75.76%,两种茶汤沉淀中酯型儿茶素总量均高于非酯型儿茶素总量,其酯型儿茶素、蛋白质、多糖和黄酮较易参与沉淀形成。因此,发酵使成品六堡茶的茶汤的胶体颗粒的稳定性增加,使其形成的茶乳酪与发酵前存在明显的差异。本研究为黑茶饮料等食品的开发提供了理论基础。     

Fenvalerate residue level and dissipation in tea and in its infusion

Fenvalerate is a non-systemic insecticide/acaricide used in controlling a wide range of pests, including those resistant to organochlorine, organophosphorus and carbamate insecticides. The study investigated the dissipation behaviour (residue level) of fenvalerate in tea and its transfer during infusion. Fenvalerate was applied on tea crop at two dosages, 100 and 200?g a.i.?ha^?1 (recommended and double the recommended) in the dry and wet seasons under field conditions. Samples (green tea shoots, made tea, its infusion and spent leaves) were analysed for fenvalerate by high-performance liquid chromatography using diode array detection. The residue dissipated faster in the wet season than in the dry season. Seven days after the treatment (normal round of plucking) the residues observed in the green shoots at the two dosages were 0.5?±?0.01, 1.1?±?0.01 and 0.4?±?0.02, 0.9?±?0.01?mg?kg^?1 in the dry and wet seasons, respectively. During processing of green tea shoots to made tea a 30–40% loss of residue was observed. The transfer of residue from made tea to infusion was in the range 10–30% for both seasons, whereas 50–70% of the residues remained in the spent leaves. However, the degradation rate in both seasons followed first-order kinetics. The half-lives were in the range of 2–3 days for green shoots and made tea in both seasons.     

微波消解-原子吸收光谱法测定昭平绿茶中微量元素

茶叶中微量元素的含量分析是茶叶科学的重要研究内容之一,其含量高低对茶叶品质影响较大,因此,有必要对茶叶中的微量元素进行测定。研究建立了以HNO3-H2O2为消解液进行微波辅助消解样品,火焰原子吸收光谱法测定绿茶中铜、铁、锌微量元素含量的方法。实验采用程序升温的方式进行样品消解,回收率高,并且对三种绿茶样品测定结果进行了比较分析。回收率在93.6%101.5%之间,RSD在0.58%3.16%之间;样品中微量元素含量分别为Fe:98.95 177.8μg/g,Zn:45.67 59.29μg/g,Cu:19.7724.22μg/g。此方法测定茶叶中微量元素,可靠、灵敏度高,选择性好,方法简便,且对环境友好,适合常规分析。     

Fenvalerate residue level and dissipation in tea and in its infusion

Fenvalerate is a non-systemic insecticide/acaricide used in controlling a wide range of pests, including those resistant to organochlorine, organophosphorus and carbamate insecticides. The study investigated the dissipation behaviour (residue level) of fenvalerate in tea and its transfer during infusion. Fenvalerate was applied on tea crop at two dosages, 100 and 200 g a.i. ha^-1 (recommended and double the recommended) in the dry and wet seasons under field conditions. Samples (green tea shoots, made tea, its infusion and spent leaves) were analysed for fenvalerate by high-performance liquid chromatography using diode array detection. The residue dissipated faster in the wet season than in the dry season. Seven days after the treatment (normal round of plucking) the residues observed in the green shoots at the two dosages were 0.5 ± 0.01, 1.1 ± 0.01 and 0.4 ± 0.02, 0.9 ± 0.01 mg kg^-1 in the dry and wet seasons, respectively. During processing of green tea shoots to made tea a 30-40% loss of residue was observed. The transfer of residue from made tea to infusion was in the range 10-30% for both seasons, whereas 50-70% of the residues remained in the spent leaves. However, the degradation rate in both seasons followed first-order kinetics. The half-lives were in the range of 2-3 days for green shoots and made tea in both seasons.     

不同干燥方式对黑茶品质的影响

目的 黑茶传统自然干燥工艺受天气、卫生、效率等因素局限,本文探讨黑茶采用现代机械干燥替代传统干燥的可行性。方法 以云南晒青毛茶渥堆叶为原料,采用不同干燥工艺(热风烘干、远红外干燥、炒干、微波干燥、光波干燥、微波光波混合干燥、晒干、晾干)制成黑茶。分析其感官品质、主要品质成分变化。结果 不同干燥方式加工的黑茶干茶色泽、汤色、叶底基本一致,香气和滋味相差较大。其中热风烘干的黑茶陈香突出,综合品质最高,其游离氨基酸含量较高。远红外干燥的黑茶滋味略带苦味,陈香较弱,其咖啡碱、儿茶素总量较低,滋味的浓度、协调度均不足。炒干的黑茶条索更紧结,香气带陈香较清新,滋味醇和,其可溶性糖、含量相对较高。微波干燥的黑茶滋味甜醇,稍带闷气,其可溶性糖、茶红素含量较高。光波干燥的黑茶茶滋味有甜醇风味及特殊香气,其游离氨基酸含量相对较高。微光波混合干燥的茶有甜醇味,香气略陈,其游离氨基酸、可溶性糖和咖啡碱的含量均介于微波与光波干燥之间,茶多酚的含量高于其他干燥方式。晒干的茶滋味涩,香气为日晒气,其游离氨基酸、可溶性糖含量较低,茶褐素含量高,儿茶素含量较高。晾干的茶滋味有涩味,口感低淡,其游离氨基酸、可溶性糖含量较低,茶褐素含量相对较高。 结论 结合感官品质和理化分析,黑茶加工干燥环节,热风烘干、炒干、微波干燥、光波干燥、微光波混合干燥等现代机械干燥方式可以取代传统的晒干和晾干方式。     

稀土在有机茶园土壤-茶叶-茶汤系统中的迁移研究

目的了解稀土在茶园土壤-茶叶-茶汤系统中的迁移情况,指导科学饮茶,为茶叶中稀土的形态研究和风险评估提供实验数据。方法采集有机茶园中的土壤及其对应茶树上的茶叶样品,经微波消解,茶叶按照日常饮茶习惯冲泡,用电感耦合等离子体质谱法(inductively coupled plasma mass spectrometry,ICP-MS)测试各样品中的稀土含量。结果土壤中约2.23%的稀土迁移到茶叶中,按照日常饮茶习惯冲泡,茶叶中约10.48%的稀土迁移到茶汤中。结论茶叶采摘期不同,产地不同,迁移率也略有不同。平均每千克茶叶中,有0.1198 mg的稀土被转移到茶汤中。     

电感耦合等离子质谱法分析不同产区信阳毛尖茶中的稀土元素

目的了解不同产区信阳毛尖茶中稀土元素含量和分布状况,并利用稀土元素对茶叶产地进行判别。方法采用微波消解样品前处理结合电感耦合等离子质谱法对信阳产区106个茶叶样品中的16种稀土元素进行测定。结果信阳毛尖茶叶中不同稀土元素含量差异较大,其中Sc、Ce、La、Nd含量较高,平均含量分别为0.4203、0.1118、0.0862、0.0457 mg/kg;不同产区信阳毛尖茶中轻稀土含量均低于重稀土含量,表明茶树在富集轻稀土元素和重稀土元素的过程中存在着差异;相关分析结果显示茶叶中16种稀土之间存在正相关,表明稀土元素在茶叶富集过程中有较强的协同作用。信阳毛尖茶中稀土氧化物的含量范围为0.5417~1.2823mg/kg,低于国家规定的限量标准2.0 mg/kg。结论稀土元素可作为信阳毛尖茶产地识别的重要指标。     

微波杀青工艺对秋季绿茶的保绿降苦作用

目的：探究微波杀青工艺对秋季绿茶的保绿降苦作用;方法：以茶树品种碧香早秋季一芽二叶茶鲜叶为原料,在传统绿茶杀青、揉捻、干燥加工工艺的基础上,将微波杀青工艺替代传统滚筒杀青工艺,按不同微波强度、微波时间设置了14组微波杀青处理,从感官品质、滋味品质、干茶与汤色色泽三个方面探究微波杀青工艺对秋季绿茶的保绿降苦作用;结果：与传统滚筒杀青工艺相比,采用微波强度500w、杀青时间为3min的微波杀青工艺,所制绿茶色绿味醇且综合感官品质最佳,其水浸出物、茶多酚、氨基酸、咖啡碱、总儿茶素、简单儿茶素的含量显著升高（P<0.05）,苦味评价指标酚/氨比、酯型儿茶素含量与总儿茶素含量的比值则显著降低（P<0.05）,且干茶与茶汤色泽在绿、明度上均有不同程度的改善;结论：利用微波杀青工艺加工秋季绿茶具有较好的保绿降苦效果,可应用于提高秋季绿茶品质的生产实践。     

Dissipation of imidacloprid in Orthodox tea and its transfer from made tea to infusion

Imidacloprid is a systemic insecticide used widely in controlling mites, mealy bugs and other related pests in fruits, vegetables and tea. The dissipation behaviour of imidacloprid residues in green tea shoots, made tea and its transfer potential from made tea to infusion in hot water was studied. Analysis in tea matrices of imidacloprid was carried out using high-performance liquid chromatography with diode array detection. Under field conditions, imidacloprid dissipation rate was found to be faster in the wet season than the dry season. Half lives in green shoots were in the range 1.14–1.23 and 1.03–1.09 days, and 1.14–1.25, 1.04–1.07 days in made tea, for the dry and wet season, respectively. The percent transfer of imidacloprid residue from made tea to infusion was in the range of 29.2–42.0% during the dry and wet season; however, 38.2% and 57.9% of the residues remained stuck to the spent leaves during the dry and wet seasons, respectively. On the basis of transfer of residues from made tea to hot water infusion, a waiting period of 7 days after pesticide application at a recommended dose for tea plucking is suggested.     

Irreversible sediment formation in green tea infusions

The formation of irreversible tea sediment (IRS) and its chemical components in green tea infusions were investigated. The results showed that the amounts of IRS in the green tea infusions from various tea cultivars ranged from 0.10 to 1.47 mg/mL. The amount of IRS was influenced remarkably by the chemical components in the green tea infusion. Principal component analysis and regression analysis indicated that gallated catechins, Mn, Ca, caffeine, Na, and (-)-gallocatechin gallate (GCG) were the principal components. IRS (mg/mL) = -4.226 + 0.275 gallated catechins + 79.551 Na + 7.321 Mn + 21.055 Ca + 0.513 caffeine - 0.129 GCG (R2 = 0.697). The contents of the main chemical components in the reversible tea sediment (RTS) and IRS were markedly different, especially the minerals. Large amount of minerals participated in the formation of irreversible green tea sediment. The amount of IRS increased with the extraction temperature.